1. Field of the Invention
The invention relates to a device for providing precise rotational motion to components of a device for intelligently directing light to a particular object in a scene and then directing the light reflected from the object into an imaging camera.
2. Background of the Invention
There are several methods, known as biometrics, used for verifying or recognizing the identity an individual. Biometric methods include analyzing a signature, obtaining and analyzing an image of a fingerprint and imaging and analyzing the retinal vascular patterns of a human eye. Recently, the art has used the iris of the eye, which contains a highly detailed pattern that is unique for each individual and stable over many years as a non-contact, non-obtrusive biometric. This technique is described in U.S. Pat. No. 4,641,349 to Flom et al. and U.S. Pat. No. 5,291,560 to Daugman. The iris identification techniques disclosed by Flom and Daugman require a clear, well-focused image of the iris portion of the eye including a well defined iris sclera boundary.
Prior to the invention described in the above-referenced, related applications and U.S. Pat. No. 5,717,512 to Chmielewski et al, there had not been an optical system which could rapidly acquire a sufficiently clear, properly aligned image of an iris of the person to be identified unless that person positioned his eye in a fixed position relatively close to an imaging camera and performed a self alignment and focus process. Such a system was introduced in those disclosures. Ideally, this system should be as unobtrusive as possible, requiring little or no cooperation by the user (except for looking in the right direction). This type of system is particularly useful in the verification of users of automated teller machines (ATMs), as well as individuals seeking access to a restricted area or facility or other applications requiring user identification.
Any optical system for iris identification of ATM users must be able to rapidly capture a clear image of the iris of the person using the automated teller machine and have the capability of performing the related processing needed for user verification or recognition. Further, such a system, especially if it is to be integrated into the ATM, must be compact in size.
In our U.S. Pat. No. 5,717,512 we describe a compact image steering and focusing device having three cameras and a tilting frame on a flat base. The tilting frame contains a pan/tilt mirror, lens system, focus motor, and pan and tilt cable drive systems, all of which can direct the field of view seen by one of the cameras. The other two cameras are mounted in fixed locations. The illuminators are also fixed and provide illumination sufficient to image an iris anywhere in the defined working volume. Although this device works well, it has limitations which prevent it from covering a larger imaging volume (i.e., one that is sufficient to image users ranging from the average 7 year old to the 95th percentile male as well as wheelchair bound individuals) in a cost effective manner. A device solving this problem was disclosed in related and copending U.S. patent application Ser. No. 09/224,544. This application focuses on certain components of that system, in particular, the precision cable drive systems used to move the apparatus about the tilt axis, to move the pan mirror about the pan axis, and to move the narrow field-of-view illuminators from side to side.
The compact image steering device disclosed in the related application can obtain a clear image of a small region on an object located in a volume bounded by an angle of 82 degrees in the vertical, an angle of 58.5 degrees in the horizontal and a radial distance from 14 inches to 30 inches in front of the optical system. The system includes a tiltable frame which carries the pan mirror and at least one camera. The position of this frame is controlled by a precision cable drive system located in the rear of the device and connected to the frame by an extended cable. Light reflected from the object of interest is captured by the mirror and directed to another camera which may or may not be on the tilting frame. Another precision cable drive system rotates the pan mirror about the pan axis. The tilt axis is substantially perpendicular to the pan axis of the mirror. The combined tilting of the frame and rotation of the pan mirror allows the mirror to be steered to any location in the imaging volume. In a preferred embodiment, a narrow field of view (NFOV) camera receives the light reflected from the pan/tilt mirror.
Two cameras are provided on the tilting frame to obtain two spatially separated but time concurrent wide field of view (WFOV) images of the subject. Images from these cameras are processed to determine the coordinates of the specific location of interest, such as the face and eyes of a person to be identified. Based upon an analysis of those images, the tilt axis and pan axis are positioned so that the mirror is adjusted to receive light reflected from the iris or other area of interest and direct that reflected light to a NFOV camera and lens system. The NFOV lens system and camera produces an image of sufficient size and quality to permit iris identification.
Illumination for the WFOV cameras is provided by attaching at least one illuminator to the tilting frame. This first illuminator is aligned so that the center axis of its respective beam pattern is parallel to the optical axis of the WFOV cameras. The beam pattern is designed so that it provides sufficient illumination coverage for the area imaged by the WFOV cameras and optics. As the tilt axis is moved up and down by the tilt axis cable drive system, the camera and illumination can image users at various heights.
NFOV illumination is provided by two illuminators which are disposed on opposite and extreme ends of the tilting frame. These illuminators"" beam patterns are significantly smaller than the WFOV illuminators beam pattern. The optical axis of these two illuminators form a plane through which the optical axis of the of the NFOV camera moves as it pans. Thus the light is directed only to the area of interest (as defined by the field of view of the NFOV camera) and energy is not wasted by illuminating an area larger than necessary The NFOV illuminators may be provided with a rotational degree of freedom so that they are able to rotate in the same direction as the pan axis. In this case, the beam pattern of one or both illuminators is steered to coincide with the location of the imaging area of the NFOV camera, as defined by the pan and tilt axes. The rotation of the illuminators is controlled via a pair of precision cable drive systems.
A control system is provided to analyze the images from the wide field of view camera and thereby specify the location of a point or area of interest on the object or person being identified. The control system provides synchronization and timing between cameras and illuminators as well and intensity control for the illuminators.